Field of the Invention
The present invention relates to a honeycomb structure, and more particularly, it relates to a honeycomb structure which is a catalyst carrier and also functions as a heater when a voltage is applied thereto, and which can inhibit an unevenness of a temperature distribution when the voltage is applied thereto and can improve a thermal shock resistance.
Background Art
Heretofore, a honeycomb structure which is made of cordierite and onto which a catalyst is loaded has been used in treatment of harmful substances in an exhaust gas discharged from a car engine. Furthermore, it is also known that a honeycomb structure formed by a silicon carbide sintered body is for use in purification of the exhaust gas (e.g., see Patent Document 1).
When the exhaust gas is treated by the catalyst loaded onto the honeycomb structure, it is necessary to raise a temperature of the catalyst up to a predetermined temperature. However, at the start of the engine, the temperature of the catalyst is low, and hence there has been the problem that the exhaust gas is not sufficiently purified.
To solve the problem, there has been investigated a method of disposing a heater made of a metal on an upstream side of a honeycomb structure onto which a catalyst is loaded, to raise a temperature of an exhaust gas (e.g., see Patent Document 2). In addition, there has been investigated a method in which a catalyst is loaded and used onto a heater made of a metal (e.g., see Patent Document 3).
Furthermore, it has been suggested that a honeycomb structure made of a ceramic material is used as “a heatable catalyst carrier” (e.g., see Patent Documents 4 and 5).